Senior Fullstack Engineer (Kotlin&React)

About the Position

Join Xebia as a Senior Fullstack Engineer specializing in Kotlin and React, leading technical discussions and developing scalable products.

Responsibilities

• Designing and developing APIs enabling integrations with external business partners
• Taking a technical lead in integration architecture and contributing to key architectural decisions
• Defining API contracts and following an API-first approach using OpenAPI / Swagger
• Developing backend services using Java and Kotlin
• Building modern web applications using React and TypeScript
• Defining and promoting software development standards and best practices
• Preparing and maintaining technical documentation
• Leading technical discussions and supporting the team in making sound engineering decisions
• Working with distributed systems and complex system integrations
• Participating in the on-call rotation

Requirements

• Strong commercial experience with Java and Kotlin
• Proven experience designing, building, and maintaining REST APIs
• Hands-on experience with API-first design and OpenAPI / Swagger
• Very good knowledge of React and TypeScript
• Solid understanding of distributed systems and system-to-system integrations
• Practical knowledge of OAuth 2.0 and OpenID Connect
• Practical experience using AI-powered assistants (e.g. GitHub Copilot, Cursor) to improve productivity, quality, or decision-making in software delivery
• Experience making architectural decisions and leading technical discussions
• Experience defining development standards and providing technical leadership within a team
• Strong communication and collaboration skills
• English at min. B2 level
• Polish at min. B1 level
• Willingness to visit the client's office in Warsaw 1–2 times per quarter
• Work from the European Union region and a work permit are required

Nice to Have

• Experience with data security and regulatory compliance, particularly GDPR
• Experience with B2B integrations and working with external business partners
• Experience applying GenAI in a more structured way within the SDLC, including defined workflows, prompt patterns, or tool integrations embedded into daily work
• Interest in and familiarity with emerging AI-driven practices (e.g. agent-based workflows, automation patterns, AI-augmented development), with a willingness to explore and experiment beyond standard approaches

We Offer

• Opportunity to work with a global AI-first, digital transformation, and engineering partner
• Be part of a team of nearly 1,000 experts in the CEE region
• Collaborate with clients such as Millennium, ING, Play, Edenred, FedEx, Leroy Merlin, Truecaller, Volotea, Schmitz Cargobull, and many more

About the Company

Xebia is a global AI-first, digital transformation, and engineering partner. With over 25 years of experience and a team of 5,000 professionals across 16 countries, we help organizations design and build scalable products, platforms, and data-driven solutions. We specialize in Artificial Intelligence, Data and Cloud, Intelligent Automation, and Digital Products, combining deep technical expertise with a strong focus on engineering excellence and a people-first culture.